1. Field of the Invention
This invention relates to a vector control device of a winding field type synchronous machine in which a field-magnet field is created by a field winding on a rotor.
2. Description of the Related Art
In vector control of winding field type synchronous machines, as shown in for example Non-Patent Document 1 below, a vector control method in which control is performed so that an armature interlinkage flux and an armature current intersect orthogonally has been used as a high efficiency, high power factor control method. In a vector control device of related art of this kind, to prevent saturation of the armature voltage occurring as a result of increasing of the induced voltage accompanying increasing of the speed of rotation, as shown in FIG. 3 of Non-Patent Document 1, so-called weak flux control in which, with reference to a motor speed ωm, at above a predetermined speed a flux command Φa* is reduced in inverse proportion to the speed, and by this means at above the predetermined speed the armature voltage is kept constant.
This is because in related art control devices of winding field type synchronous machines, voltage drop due to resistance has been ignored. However, in synchronous machines driven at low voltages and high currents, like winding field type synchronous machines for use in automotive vehicles, the proportion of the armature voltage constituted by voltage drop due to resistance may be large. In this case, the armature voltage fluctuates greatly not only with the flux but also with the armature current. As means for resolving this issue, for example technology set forth in Patent Document 1 below has been disclosed. In the technology disclosed in Patent Document 1, when an armature voltage command has risen above a predetermined value the flux command is corrected.
And, in a winding field type synchronous machine, because currents flow through both an armature winding and a field winding, a loss occurs in both windings. Consequently, to maximize the efficiency of a winding field type synchronous machine, it is necessary to optimize the currents flowing through both of the windings. As means for resolving this issue, for example technology set forth in Patent Document 2 below has been disclosed. In the technology disclosed in Patent Document 2, from a torque command and the speed of the synchronous machine supplied to the control device, armature current command values for a field flux direction (d axis) and a direction orthogonal to that (q axis), and a field flux command value, such that the efficiency is maximum in that operating state, are obtained from tables. Similar technology is also disclosed in Patent Document 3 below, and in Patent Document 3 a field current command is obtained from a table instead of a field flux command.
Non-Patent Document 1: “Vector Control of Synchronous Machine”, Hiroshi OSAWA, at S.8–19, 1989 National Convention Record of The Institute of Electrical Engineers of Japan Patent Document 1: Japanese Patent Publication No. 2856950 ([0004] to [0015], FIG. 1)
Patent Document 2: JP-A-8-331900 ([0046] to [0047], FIG. 14)
Patent Document 3: JP-A-11-313498 ([0035] to [0038], FIG. 5)
In a vector control device of a winding field type synchronous machine of related art, when the armature voltage command has risen above a predetermined limit value the flux command is corrected and the armature voltage is limited, and when the armature voltage command does not exceed the predetermined value the armature voltage remains below the predetermined limit value without the flux command being corrected. On the other hand, in a case where as shown in Patent Document 1[0004] to [0009] a current command is calculated from a flux command using a motor constant of the synchronous machine, when due to magnetic saturation or the like there is a difference between the set value and the actual value of the motor constant, it may happen that the flux corresponding to the flux command cannot be created. In particular, when the set value of inductance is greater than the actual value, there has been the problem that the actual flux is low with respect to the flux command and as a result the armature voltage falls and the ratio of the armature voltage to the armature power supply voltage (i.e. the percentage power supply utilization) is low.
On the other hand, in a vector control device of a winding field type synchronous machine of related art, as mentioned above, command values of a d-axis current, a q-axis current and a field are obtained with reference to tables using a torque command and a speed, and the data of these tables is created in advance by calculation using characteristic parameters of the synchronous machine that is the control object, for example as set forth in [0037] to [0046] of Patent Document 1. However, these current command values at which the efficiency of the synchronous machine is maximal vary with fluctuations in the winding resistances with motor temperature and the usable power supply voltage, and in preparing tables of current command values corresponding to these factors there have been the problems that the amount of data is large and storing it in the control device is not easy, and that a great deal of labor is needed for their creation.